Pasteurization does reduce some nutrients, but the losses are smaller than most people expect. Standard pasteurization of milk preserves the vast majority of its calories, protein, calcium, and most vitamins. The nutrients most affected are certain heat-sensitive vitamins (especially vitamin C), some beneficial proteins involved in immune function, and naturally occurring bacteria. Minerals like calcium and phosphorus come through essentially unchanged.
The degree of nutrient loss depends heavily on the type of pasteurization, the food being heated, and which specific nutrient you’re asking about. Here’s what actually happens to each category.
Minerals Stay Intact
Calcium, phosphorus, and other minerals in milk are not meaningfully affected by heat treatment. Multiple studies comparing raw milk, standard pasteurized milk (HTST), and ultra-high temperature (UHT) milk have found no significant difference in calcium bioavailability. In animal studies using radioactive calcium tracers to precisely measure absorption, no effect was attributable to heat treatment. This held true across every pasteurization method tested.
The same result appeared in studies on human infants. Low birth-weight preterm babies fed raw human milk and babies fed heat-treated human milk absorbed and retained the same amounts of calcium, phosphorus, and sodium. If your concern about pasteurization is calcium, there’s no meaningful loss to worry about.
Vitamins Vary Widely
Not all vitamins respond to heat the same way. Riboflavin (B2), one of the key vitamins in milk, is stable through pasteurization. It melts and decomposes only above 278°C, far beyond any pasteurization temperature. Riboflavin is, however, extremely sensitive to light: about 30% is destroyed by sunlight within just 30 minutes. So the opaque carton your milk comes in protects more riboflavin than skipping pasteurization would.
Vitamin C is a different story. It’s highly heat-sensitive and oxidizes easily. In fruit juice production, pasteurization losses range from modest to dramatic depending on temperature and duration. Pasteurizing blackcurrant nectar at 80°C for 27 seconds cost only 2 to 6% of its vitamin C. But pasteurizing strawberry juice at 85°C reduced vitamin C by about 35%. Apple juice pasteurized at 90°C for four minutes retained only 11% of its original vitamin C. Tomato processing at 100°C destroyed roughly 80% of the vitamin C in both red and yellow varieties.
The pattern is consistent: higher temperatures and longer processing times destroy more vitamin C. Cow’s milk is not a major source of vitamin C to begin with, so this loss matters more for juices and other fruit products.
Protein and Enzyme Changes
Pasteurization doesn’t destroy the basic nutritional value of milk protein. Your body still digests and absorbs the amino acids. What changes is the structure of certain specialized proteins, particularly whey proteins and immune-related compounds.
Standard HTST pasteurization (72°C for 15 seconds) denatures roughly 8% of beta-lactoglobulin, the main whey protein in cow’s milk. That’s a minor structural change. UHT processing, which uses much higher temperatures, denatures significantly more. At 90°C, measurable beta-lactoglobulin remains, but above 100°C, very little survives in its native form.
Enzymes naturally present in milk are also affected. Alkaline phosphatase is completely inactivated by pasteurization (its absence is actually used as the standard test to confirm milk has been properly pasteurized). Plasmin, a protein-digesting enzyme, is also inactivated. These enzymes play roles in milk’s natural biology but aren’t considered nutritionally essential for the person drinking it.
Immune Proteins Take the Biggest Hit
The most significant nutrient losses from pasteurization involve immune-active proteins, and this matters most in the context of human breast milk. Holder pasteurization of donor breast milk (the standard method used in milk banks) reduces IgA antibodies by about 30% and IgG antibodies by about 60%. These are proteins that help protect infants from infection.
In cow’s milk, UHT processing destroys about 97% of immunoglobulin G (IgG) and about 71% of lactoferrin, an iron-binding protein with antimicrobial properties. Standard HTST pasteurization causes much less damage to these proteins. The general rule: the more intense the heat treatment, the greater the loss of these bioactive compounds.
Beneficial Bacteria Are Eliminated
Pasteurization is designed to kill bacteria, and it doesn’t distinguish between harmful and helpful ones. Raw milk naturally contains lactic acid bacteria, including Lactobacillus and Bifidobacteria species, which can benefit gut health. These are wiped out during pasteurization.
This matters most for infant nutrition. Infants fed pasteurized donor breast milk develop gut microbiomes that differ significantly from those fed their mother’s own milk, with lower levels of Bifidobacteria and higher levels of less desirable bacteria like Staphylococcus. Researchers are actively exploring ways to recolonize pasteurized donor milk with beneficial bacteria to close this gap. For adults consuming cow’s milk, the loss of these bacteria is less consequential since the bacterial counts in raw milk are relatively low compared to fermented foods like yogurt or kefir.
Fat Changes Are Small but Real
Pasteurization does alter milk fat, though the changes are modest. Heat treatment reduces overall fatty acid concentrations, with both saturated and polyunsaturated fats (PUFAs) declining. The largest reductions among PUFAs were in the range of 8 to 10%, affecting omega-3 fatty acids like alpha-linolenic acid (down about 9.6%) and EPA (down about 8.2%), as well as certain omega-6 fatty acids. These reductions are caused by oxidation and chemical rearrangement during heating.
While any loss of omega-3s is worth noting, milk is not most people’s primary source of these fats. If you’re relying on fatty fish, flaxseed, or walnuts for omega-3 intake, the small reduction in milk fat from pasteurization has little practical impact on your overall diet.
HTST vs. UHT: Intensity Matters
The two most common pasteurization methods affect nutrients quite differently. HTST (high-temperature short-time) heats milk to about 72°C for 15 seconds. UHT (ultra-high temperature) heats it to 135 to 150°C for a few seconds, producing shelf-stable milk that doesn’t need refrigeration.
HTST and the older batch method (LTLT, which heats to about 63°C for 30 minutes) have relatively little impact on whole milk’s nutritional profile. UHT processing causes substantially more protein denaturation and greater losses of immune-active compounds. The tradeoff is a much longer shelf life, which reduces food waste and makes milk accessible in areas without reliable refrigeration.
For juices, the same principle applies. Orange juice pasteurized at 90°C for one minute retained about 82% of its vitamin C. Newer non-thermal methods like pulsed electric fields retained 95% or more. The food industry is increasingly using these alternatives specifically because they preserve more heat-sensitive nutrients while still making products safe.
Putting the Losses in Perspective
The nutrients most people drink milk for, protein, calcium, riboflavin, and calories, survive pasteurization with minimal or zero loss. The nutrients that take the hardest hit are immune proteins, beneficial bacteria, and certain heat-sensitive vitamins, which matter most in specialized contexts like donor breast milk for premature infants. For everyday cow’s milk, the nutritional difference between raw and pasteurized is small enough that multiple review studies have concluded it has no practical significance for mineral absorption or protein quality. Choosing HTST-pasteurized milk over UHT when possible, and storing it away from light, does more to preserve its nutritional value than most people realize.